It has been common practice, particularly in the case of internal grinding machines, to operate the cross-feed portion of a grinding cycle by use of an electrical stepping motor which is energized by electrical pulses. The pulses are produced by a pulse generator and a control operates between the generator and the stepping motor to present the stepping motor with the pulses in various modes, frequencies, and amounts. This makes it possible to select from an almost endless variety of grinding cycles. Because the counting equipment available for counting the pulses is so reliable, it is possible to operate the grinding machine on the "dead reckoning" principle (as it is called in the art of the ocean navigation), rather than to take readings at certain intervals to determine the location of the grinding wheel relative to the workpiece. Such controls for the pulses have had some shortcomings however and one problem is that, when a setting of the feed rate is made on the face of the grinding machine, the setting device must consist of a warped potentiometer or a calibrated form of pulse-rate control. This is because in the past an equal change in resistance at the face of the control box results in a non-linear or exponential change in the frequency output of the generator. Another difficulty that has been experienced is that, as the diamond begins to wear, the fact that the infeed distance begins to change becomes troublesome. For instance, in an "interrupt to dress" cycle, the wheel is backed off from the workpiece far enough so that the wheel can pass over the diamond for a dress. After the dressing operation is finished, sufficient pulses are introduced into the grinding wheel to advance it into contact with the workpiece again for the finish grind. As the diamond wears, this advance or diamond clearance is too small and the wheel is liable to strike the workpiece while it is moving at a fairly rapid rate and can cause damage. Therefore, the ordinary operator must set up his "diamond clearance" or index large enough so that this will not happen even when the diamond wears. Such a large diamond clearance means that the machine converts to a slower rate of feed long before the wheel reaches the workpiece and this is a waste of machine time. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a grinding machine using the stepping motor feed in which pulse rate and, therefore, the feed can be closely and easily controlled.
Another object of this invention is the provision of a grinding machine having an adjustable diamond clearance, which clearance is adjusted in accordance with the wear on the diamond.
A further object of the present invention is the provision of an internal grinding machine of the stepping-motor type in which the frequency of the electrical pulses presented to the stepping motor for feed and the number of such pulses presented for diamond clearance purposes are carefully regulated.
It is another object of the instant invention to provide a grinding machine whose grinding cycle over a large number of workpieces averages out to a lesser amount of time than in the prior art.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.